Rheostat



Nov. 20, 1951 s. RICHMANI ET'AL RHEOSTAT 2 SHEETS-SHEET 1 Filed March 2, 1949 INVENTOR. flM l/EL L.

11 TTOR NE Y Patented Nov. 20, 1951 RHEOSTAT Samuel L. Richman, White Plains, and Arthur Fitchman, Yonkers, N. Y., assignors to Sonotone Corporation, Elmsforzl, N. Y., a corporation of New York Application March 2, 1949, Serial No. 79,194

3 Claims. 1

This invention relates to rheostat devices, and more particularly to rotary rheostat or potentiometer devices of the general type used in hearing aids, radio receivers, and other devices requiring small compact rheostats.

Among the objects of the invention is a novel rheostat device of the foregoing type which is extremely small and compact and assures that the frictional forces resisting rotary motion or displacement of the rotary rheostat member from the desired setting are controlled independently of any forces determining the pressure with which the slider contact is resiliently biased into contact engagement with different peripheral portions of the resistance element of the device.

The foregoing and other objects of the invention will be best understood from the following description of exemplifications thereof, reference being had to the accompanying drawings, where m:

Fig. 1 is a plan view of the inner side of the rheostat shown in Fig. 2, with the bottom wall removed;

Fig. 2 is a cross-sectional view of the rheostat device, along the lines 22 of Fig. 1;

Fig. 3 is a plan view of the inner side of the bottom wall member of the rheostat of Figs. 1 and 2;

Fig. 4 is a cross-sectional view along the lines 4-4 of Fig. 1;

Fig. 5 is a view similar to Fig. l of another form of rheostat device of the invention, as shown in Fig. 6; and

Figs. 6 and 7 are cross-sectional views along lines 6-45 and l! of Figs. 5 and 6, respectively.

The rheostat devices shown were invented for use as a part of a wearable amplified hearing aid having extremely small overall dimensions, small enough to fit into a vest pocket of a person.

Referring to Figs. 1 to 4, the rheostat exemplifying one form of the invention is made in the shape of a tiny fiat casing structure comprising a rotary wall member H and a supporting wall member l2, which are rotatably joined to each other along a central axis. In the form shown, the casing structure in which all the operating parts are housed has an outer diameter of only .750 inch and its overall height is only .250 inch. The cooperating casing wall members H and 12 are made of plastic or moldable insulating material andare designed to interfit and to prevent dust, dirt or other foreign matter from entering the interior space i3 of the casing, while permitting revolvable motion between the rotary wall member 5 I and the supporting wall member 12. In the form shown, this is accomplished by providing the rotary wall member I l with a circular border wall l4 overlapping a flanged circular rim portion I5 of the supporting wall member I2.

The two casing wall members H and I2 are shown provided with a revolvable junction structure comprising two interfitting cooperating junction members I? and I8 of metal, extending from the central portions of the two casing wall members H and 52, respectively. The junction member ii is shown in the form of a pin or shaft having an enlarged flanged head with a hollow rivet extension 21 seated and affixed in the obvious way shown to the rotary wall member ll, within its central opening portion, so that it forms a fixed part thereof. The cooperating junction member I8 is shown formed of a hollow cylindrical bushing provided along an intermediate portion thereof with an enlarged flange portion 23 seated and afiixed to the central portion of the supporting wall member l2 within its central opening. The flanged portion 23 of the bushing l8 has a hollow rivet extension serving to affix and secure the hollow bushing member [8 to an interfitting shoulder portion of the wall member l2, so that the junction member bushing i8 forms a fixed part of the supporting Wall member 12.

As seen in Figs. 1 and 2, the wider flanged por' tions l9 and 23 of the junction shaft l1 and junction bushing 18 are of hexagonal shape, so that by their engagement with correspondingly shaped portions of their seating openings of the two casing wall members II and i2 they are affixed against rotation relative to the wall members to which they are secured. The two wall members are readily assembled by simply slipping the shaft member ll of the wall member I i into the axial journaling opening of the bushing sleeve I8, the shaft il being retained in its position by a, split spring ring 26 sprung into the locking groove formed in the end of the pivot shaft IT. The exposed outer end portion of the bushing i8 is provided with a thread making it possible to secure it, as by a nut, in its position on a chassis or frame of a device in which it is to be used.

Within the interior of the rheostat casing is mounted an arcuate or ring-shaped resistance element 3| carried by one wall member and arranged for cooperation with a contact element 32 of a contact arm structure 33 carried by the,

other wall member, so that by rotating one of it the wall members relative to the other, the contact element 32 will slide and maintain good electrical contact engagement with the diiierent peripheral portions of the ring-shaped resistance element 3I. The arcuate resistance element 3! is of the conventional type and may consist of a circular strip of: electrically insulating 'material coated with a film of resistance material. Al-- ternatively, the entire body of the ring-shaped resistance element 3I may be made of a resist-'- ance material. As a further alternative, an arouate surface portion of the inner surface of the support wall member I2 may be coated with a film of resistance material to provide the resistance element. In the form shown, the resistance element 35 is arranged to form a fixed inwardly exposed arcuate resistance element of the support wall member I2, arranged to be engaged by the contact element 32in each of its different angular portions thereof.

Thecontact arm structure 331s made ofv a suitable electrically conducting spring metal, such as-beryllium or copper, provided with a cone tral seating collar 3t having a flange 36*witha circular opening by means of which it seatedon the inwardly projecting bushing portion 25' of -the supporting wall member I2 for rotation around'it. In the particular device shown iniFlg'.

I l, the contact'arm'structure 33Iextending from its seating collar 3 i is made in the form of an arcuate 100p .providedat its outer endwith a socket portion 35 holding L therein the contact element 132 which is pressed against theresistance element. 3I. The. elasticbody. ofthe contact structure 33', S I-isdeformed so'that when its'oole lar 34 -is.retained in'sthe central position shown, resting with its central portion against the flange 23 of the'bushing member I8; the contact arm structure 33 "will be elastically deformed and vex-. ert" on iitS contact element 32: elastic restoring forces whichisubject the contact element to contact forces .of :audesiredsmagnitude' for maintains ing proper; electrical sliding contact connectionwith;difierent.:peripheral elements of: the-ringshaped resistance .element 3 I, depending -,on the angularuposition of .the arm structure '33,

In the particular rheostat structure shown in Figs.11;t-4, thelcontact arm structure'te :is held affixed for rotation with the rotary wall member II by the engagement of a rearwardly, extending retainerrarm 37 within a locking recess 38 provided on the inwardlyfacing surface'of :the'rotary wall member I I. r

The rotary wall member isshowniprovided with small inward projections or bosses 4| shaped to ;:deflect facing ;arm portions of athe arm structure;-33 in the direction toward the-cooperating spending to the .arcuatelength of the resistance element 3 I.

A- connector pin it of metal, molded in the support wall member I I, provides a. terminal connection toponeend oflthe resistance element 3I.

- In 1a.;rheostat of thectype?described; itiis1-.de.-

siredcthat therrotar y wall members should :be =.re-e tained in any oneof the difierent peripheralset-t tings of its contact element 32. Heretofore, such rheostat devices depended on the elastic forces exerted by the contact arm and its contact element on the resistance element for retainin the contact element in its different peripheral setting and for resisting displacement of the two rotatably joined rheostat members." However, such prior. art'rheostat devices havesalwaysbeen a source of trouble because, when designed to re tain the contact arm in the different selected settings, the pressure exerted by the contact element on the resistance element had to be made relatively large, with the result that the resistance element and-thecontact element had to be subjected torexcessive wear.

According to the invention, the difiiculties connected with such prior art rheostats are eliminated by providing an independent resilient biasingfmeans to control the magnitude of the frictional forces resisting rotation of the two revolvably joinedurheostat members of; such :rheostat devices, makinglit possible to providesfor independent control of the resilient forces :exerted by the contact element on theresistance element.

The additional independent rotaryamotion COD! trol means of the invention is so 'combined :with the other elements. of such rheostat device as to make it unnecessary to increase its-overall di mensions and withoutmaterially addingto its manufacturingscostsr In. the form of the device shown in Figs-l toe, the additional motion controlling .spring means is suppliedoyv a conventional elastically-come pressed I helical coil springJE-i placedsurrounding bushingportion.25.oflmember I2 andheldcompressed between .the inner. surface portion of the rotary wall member II andthe-circularcentral collar flange 35 of the contact arm 33,.for pressing the rotating ,collanfiange .36 against 11118116111 tral portion ofthe fixed wall member IZand. providing the desiredrindependent rotation-ma sisting, forces. With'lsuch' an arrangement, the

helical'contact spring 45 may be readily'given.

the desired spring action by elongating it or shortening it in production, .so thatwhen it'is placed in position around the junction structure, it willmpress the collarflange 3! carried by the rotary" wall" member I I' with a definite force against .the facing central metal flange 23 offthe fixed wall member I2 to providetherebetween a controlled frictional engagement resistingarcuate displacement of the rotary wall. member II from one rheostat contact position to 'anotherwith-i out in anyway modifying the forceswith which theelasticallydeformed arm elements of the con-o tactarm structure 33 hold the contact ele'mentBI in sliding contact engagement withanarcuate portion of the rheostat element 3|.

Figs 5, 6 and "7 show a rheostat device of the invention generallysimilarto that of Figs. l'to lj but provided with another form of spring means suppyling' independent motion-resisting forces restraining the two rheostat Wall members against displacement from an adjusted rheostat position without modifying the spring forces which maintain the desired contact pressure between the contact arm and the arcuateiresist 1 to .4. I g

. In the "rheostat device of- Figs.t5, 6 and'7, ,.two

deflector-projections. 2-.'-I extending; from the inner :surface 201% :the: rotaryywall ;m'ember:. Ze-i I serve to elastically deflect the two arcuate arm portions of the contact arm structure 2-33 for providing the desired elastic biasing force of the spring contact arm structure 33, maintaining the desired sliding contact pressure between its contact element 2-32 and the facing portion of the arcuate resistance element 2-3l.

The spring arm structure 2-33 has a collar portion 2-34 seated around the inner bushing portion 2-25 of the fixed wall member 2-12 and resting against its underlying metallic bushing flange 2-25. The independent rotary motionresisting action is provided by a spring member of sheet metal generally designated 6|. The spring member 6| has a plurality of spring arms 62 engaging with their ends inward seating recesses 63 of the rotary wall member 2-H for pressing a central collar portion 64 of the spring member 6| against the underlying circular collar 2-34 of the contact arm structure 2-33 with a desired independent control force fixing the frictional forces which resist arcuate deflection of the contact arm all member 2-1 I with its contact arm structure 2-33 from a desired adjusted position.

The principles of the invention explained in connection with specific exemplifications thereof will suggest to those skilled in the art many other applications and modifications of the same. It is accordingly desired that, in construing the breadth of the appended claims, they shall not be limited to the specific details shown and described in connection with exemplifications thereof.

What is claimed is:

1. In a rheostat device: a contact actuating wall structure having an integral central metallic junction member and a rheostat wall structure having an integral central metallic junction member; said two wall structures having inwardly facing surfaces and interfitting circular border portions surrounding said inwardly facing surfaces and confining between them a shallow generally circular interior space; one of said junction members being rotatably seated in a coaxial seating opening of the other of said two Junction members and extending beyond the opposite ends of said other of said junction members and forming therewith a metallic junction structure rotatably joining said two wall structures; the junction member of said rheostat wall structure having a central inwardly facing circular guide surface and said rheostat wall structure having a relatively fixed inwardly facing resistance element generally concentric with said junction structure; a rotatable electrically-conducting contactor structure having a central fiat circular collar element surrounding said junction structure and engaging said circular guide surface and a resilient contact arm structure extending from said collar and including a contact element resiliently urged by said arm structure into sliding contact engagement with different peripheral portions of said resistance element; said contact structure having a retainer arm extending from said collar diametrically opposite from said contact arm element into interlocking engagement with a recessed portion of said actuating wall for rotation therewith; and an independent spring structure encircling said junction member and held compressed between an inwardly facing surface of the junction member of said actuating wall structure and the facing circular surface of said collar compressing said collar into frictional contact engagement with said circular guide surface of the junction member of said rheostat wall structure for controlling the frictional forces resisting rotary motion of one wall structure relative to the other wall structure without substantially modifying the resilient forces exerted by said contact arm structure on said resistance element.

2. In a rheostat device as claimed in claim 1, said spring structure being formed of a coil spring having an end coil turn engaging the facing surface of said collar, the opposite coil end turn of said spring engaging a facing circular surface portion of said actuating wall structure.

3. In a rheostat device as'claimed in claim 1, said spring structure formed of a resilient spring sheet member having a central collar portion overlying the central collar element of said contact structure and a plurality of spring arms extending toward interengagement with inwardly facing surface portions of said actuating wall structure.

SAMUEL L. RICHMAN. ARTHUR FITCHMAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,356,634 Koch Oct. 26, 1920 2,145,953 Schellenger Feb. '7, 1939 2,346,598 Mucher Apr. 11, 1944 2,451,241 Rosentreter Oct. 12, 1948 

